The present invention relates to a so-called three-electrode-type alternating-current-driven-type plasma display having pairs of sustain electrodes and address electrodes.
As an image display device that can be substituted for a current mainstream cathode ray tube (CRT), flat-screen (flat-panel) displays are studied in various ways. Such flat-panel displays include a liquid crystal display (LCD), an electroluminescence display (ELD) and a plasma display (PDP). Of these, the plasma display has advantages such as a relative easiness to form a larger screen and attain a wider viewing angle, excellent durability against environmental factors such as temperatures, magnetism, vibrations, etc., and a long lifetime. It is therefore expected that the plasma display can be applied not only to a home-use wall-hung television set but also to a public large-sized information terminal.
In the plasma display, a voltage is applied to discharge cells charged with a discharge gas, such as a rare gas, and a phosphor layer in the discharge cell is excited with an ultraviolet ray generated by glow discharge in the discharge gas to emit light. That is, each discharge cell is driven according to a principle similar to that of a fluorescent lamp, and generally, the discharge cells are put together on the order of hundreds of thousands to constitute a display screen. The plasma display is largely classified into a direct-current driven type (DC type) and an alternate-current driven type (AC type) according to the methods of applying a voltage to the discharge cells, and each type has advantages and disadvantages. AC-type plasma displays are commercially produced and constitute a mainstream in the market.
FIG. 15 shows a typical constitution of a conventional AC-type plasma display. This AC-type plasma display comes under a so-called three-electrode type, and discharge is caused by a pair of sustain electrodes 112 and an address electrode 122. In the AC type plasma display shown in FIG. 15, a first panel 110 corresponding to a front panel and a second panel 120 corresponding to a rear panel are bonded to each other in their circumferential portions. Light emission from a phosphor layer 125 on the second panel 120 is viewed, for example, through the first panel 110.
The first panel 110 comprises a transparent first substrate 111, sustain electrodes 112 made of a transparent electrically conductive material and formed in the form of a stripe on the first substrate 111, bus electrodes 116 made of a material having a lower electric resistivity than the sustain electrodes 112 and provided for decreasing the impedance of the sustain electrodes 112, and a protective layer 117 made of a dielectric material and formed on the first substrate 111, the bus electrodes 116 and the sustain electrodes 112. The protective layer 117 is constituted of two layers such as a dielectric material layer and a covering layer that are positioned in this order from the first substrate side, while it is shown as a single layer.
The second panel 120 comprises a second substrate 121, address electrodes (also called xe2x80x9cdata electrodesxe2x80x9d) 122 formed in the form of a stripe on the second substrate 121, a dielectric material film 123 formed on the second substrate 121 and the address electrodes 122, insulating separation walls 124 which are formed in regions on the dielectric material film 123 between neighboring address electrodes 122 and extend in parallel with the address electrodes 122, and phosphor layers 125 each of which is formed on the dielectric material film 123 and on side walls of the separation wall 124. The phosphor layers 125 are composed of a red phosphor layer 125R, a green phosphor layer 125G and a blue phosphor layer 125B, and these phosphor layers 125R, 125G and 125B for corresponding colors are arranged in a predetermined order. FIG. 15 shows a partial exploded perspective view, and an actual embodiment; and, top portions of the separation walls 124 on the second panel side are in contact with the protective layer 117 on the first panel side. A region where a pair of the sustain electrodes 112 and the address electrode 122 positioned between the two neighboring separation walls 124 overlap corresponds to one discharge cell. And, a rare gas is sealed in each space surrounded by the neighboring separation walls 124, the phosphor layer 125 and the protective layer 117.
The extending direction of projection image of the sustain electrode 112 and the extending direction of projection image of the address electrode 122 cross each other at right angles, and a region where a pair of the sustain electrodes 112 and one set of the phosphor layers 125R, 125G and 125B overlap corresponds to one pixel. Since glow discharge takes place between a pair of the sustain electrodes 112, a plasma display of the above type is called a xe2x80x9csurface discharge typexe2x80x9d. A pulse voltage lower than the discharge start voltage of the discharge cell is applied to the address electrode 122 immediately before the application of a voltage to a pair of the sustain electrodes 112, whereby a wall charge is accumulated in the discharge cell (selection of a discharge cell for display), so that the apparent discharge start voltage decreases. Then, discharge that starts between a pair of the sustain electrodes 112 can be sustained at a voltage lower than the discharge start voltage. In the discharge cell, the phosphor layer excited by irradiation with vacuum ultraviolet ray generated by glow discharge in the rare gas emits light in a color inherent to the phosphor material. The vacuum ultraviolet ray that is generated has a wavelength dependent upon the sealed rare gas.
The light emission state of glow discharge in the discharge cell will be explained below with reference to FIGS. 13A, 13B, 14A and 14B. FIG. 13A schematically shows a light emission state when DC glow discharge is carried out in a discharge tube with a rare gas sealed therein. From the cathode to the anode, an Aston dark space A, a cathode glow B, a cathode dark space (Crookes dark space) C, a negative glow D, a Faraday dark space E, a positive column F and an anode glow G consecutively appear. In AC-glow discharge, a cathode and an anode are repeatedly altered at a predetermined frequency, so that the positive column F is positioned in a central area between the electrodes and the Faraday dark spaces E, the negative glow D, the cathode dark spaces C, the cathode glow B and the Aston dark spaces A consecutively appear symmetrically on both sides of the positive column F. The state shown in FIG. 13B is observed when the distance between the electrodes is sufficiently large like a fluorescent lamp. As the distance between the electrodes is decreased, the length of the positive column F decreases. When the distance between the electrodes is further decreased, the positive column F disappears, the negative glow D is positioned in the central area between the electrodes, and the cathode dark spaces C, the cathode glow B and the Aston dark spaces A appear symmetrically on both sides in this order as shown in FIG. 14A. The state shown in FIG. 14A is observed when the distance between the electrodes is a state that can be attained in a conventional general AC-type plasma display.
Meanwhile, in the conventional AC-type plasma display shown in FIG. 15, pairs of the sustain electrodes 112 are formed on one plane. The distance between one sustain electrode 112 and the other sustain electrode 112 of each pair is therefore required to be a predetermined gap (d), for example, for causing the negative glow discharge. The above gap (d) is defined by Paschen""s law that a discharge start voltage Vbd can be expressed by the function of the product d-p of the gap (d) and the gas pressure (p), and it is generally at least 100 xcexcm in the negative glow discharge. Further, the sustain electrodes 112 are required to be tens of microns or more for decreasing the impedance thereof.
When the distance from one discharge cell to another neighboring discharge cell is 200 xcexcm, when each sustain electrode 112 has a width of 60 xcexcm and when the gap (d) of the sustain electrodes is at least 70 xcexcm, the discharge cell pitch comes to be 390 82 m or more. In such a structure, the largest distance between one sustain electrode 112 and another neighboring sustain electrode 112 comes to be 190 xcexcm, which is a distance sufficient for causing a negative glow discharge. Further, in an AC-type plasma display having the conventional structure, it is difficult to produce an AC-type plasma display in which the pixel pitch is smaller than 390 xcexcm when attainable brightness is taken into account.
It is therefore an object of the present invention to provide an alternating-current-driven-type plasma display which makes it possible to decrease the size of each pixel, i.e., the size of each discharge cell.
According to the present invention, the above object of the present invention is achieved by an alternating-current-driven-type plasma display (to be simply referred to as xe2x80x9cplasma displayxe2x80x9d hereinafter) having a first panel and a second panel,
said first panel comprising,
(A) a first substrate,
(B) a first sustain electrode formed on the first substrate,
(C) a first separation wall that is formed on the first substrate and extends in a first direction, and
(D) a second sustain electrode formed on an upper portion of a side wall on one side of the first separation wall and spaced from the first sustain electrode, and
said second panel comprising,
(a) a second substrate,
(b) a second separation wall that is formed on the second substrate and extends in a second direction different from the first direction in which the first separation wall extends,
(c) an address electrode formed on the second substrate, and
(d) a phosphor layer formed on or above the address electrode.
The plasma display of the present invention is a so-called three-electrode-type plasma display. In the plasma display of the present invention, the first panel and the second panel are arranged so as to face each other such that pairs of the sustain electrodes (the first sustain electrode and the second sustain electrode) and the address electrode face each other. For structural simplification of the plasma display, preferably, the first direction and the second direction make an angle of 90 degrees.
A discharge cell is constituted of a pair of the first separation walls formed on the first substrate, a pair of the second separation walls, and the first and second sustain electrodes, the address electrode and the phosphor layer which occupy a region surrounded by the above first and second separation walls.
The plasma display of the present invention may have a constitution in which the address electrode extends in the second direction. In this constitution, the first sustain electrode may extend in the second direction. The plasma display having the above constitution will be referred to as the xe2x80x9cplasma display having the first constitution of the present inventionxe2x80x9d for convenience. The first separation wall is formed across the first sustain electrode. Alternatively, there may be employed a constitution in which the first sustain electrode extends in the first direction. The plasma display having such a constitution will be referred to as the xe2x80x9cplasma display having the second constitution of the present inventionxe2x80x9d for convenience. In the plasma display having the first or second constitution of the present invention, the first panel may further have a third separation wall that is formed on the first substrate and extends in the second direction. That is, the first and third separation walls are formed on the first substrate in the form of a lattice. In the plasma display having the first constitution of the present invention, the third separation wall is formed across the second sustain electrode. In the plasma display having the second constitution of the present invention, the third separation wall is formed across the first and second sustain electrodes.
Alternatively, the plasma display of the present invention may have a constitution in which the first panel further has a third separation wall that is formed on the first substrate and extends in the second direction, the first sustain electrode extends in the second direction, and the address electrode extends in the first direction. The plasma display having the above constitution will be referred to as the xe2x80x9cplasma display having the third constitution of the present inventionxe2x80x9d for convenience. In the plasma display having the third constitution of the present invention, the first and the third separation walls are formed on the first substrate in the form of a lattice. In this case, the third separation wall is formed across the second sustain electrode, and the second separation wall is formed across the address electrode.
In the plasma display having the first or second constitution of the present invention, the second sustain electrode extends in the first direction, and the address electrode extends in the second direction. Therefore, when a voltage is applied to the second sustain electrode and the address electrode, a discharge cell having an overlap of the second sustain electrode and the address electrode is selected as a discharge cell to discharge. In the plasma display having the third constitution of the present invention, both the second sustain electrode and the address electrode extend in the first direction. Therefore, when a voltage is applied to the second sustain electrode and the address electrode, discharge cells on an entire one line are selected as discharge cells to discharge, and as a result, an optical crosstalk is liable to take place between the neighboring discharge cells. The above crosstalk can be reliably prevented when the third separation wall extending in the second direction is formed on the first substrate.
In the plasma display of the present invention, preferably, the distance (L1) between the first sustain electrode and the address electrode is 1xc3x9710xe2x88x925 m to 4xc3x9710xe2x88x924 m, desirably 5xc3x9710xe2x88x925 m to 2xc3x9710xe2x88x924 m, and the distance (L2) between the second sustain electrode and the address electrode is 5xc3x9710xe2x88x926 m to 3xc3x9710xe2x88x924 m, desirably 2xc3x9710xe2x88x925 m to 1.5xc3x9710xe2x88x924 m. When the distance (L1) between the first sustain electrode and the address electrode is set to be 1xc3x9710xe2x88x925 m to 4xc3x9710xe2x88x924 m, a sufficient space (which will be called xe2x80x9cdischarge spacexe2x80x9d) surrounded by a pair of the first separation walls formed on the first substrate and a pair of the second separation walls formed on the second substrate can be secured. Further, when the distance (L2) between the second sustain electrode and the address electrode is set to be 5xc3x9710xe2x88x926 m to 3xc3x9710xe2x88x924 m, a sufficient thickness can be secured for the phosphor layer.
Preferably, the distance (L0) between the first sustain electrode and the second sustain electrode is 5xc3x9710xe2x88x926 m to 3xc3x9710xe2x88x925 m, desirably, 1xc3x9710xe2x88x925 m to 2xc3x9710xe2x88x925 m. When the distance (L0) between the first sustain electrode and the second sustain electrode is 5xc3x9710xe2x88x926 m to 3xc3x9710xe2x88x925 m, cathode glow discharge comes to be predominant as glow discharge.
The space (discharge space) surrounded by a pair of the first separation walls formed on the first substrate and a pair of the second separation walls formed on the second substrate is charged with a rare gas and sealed, and the phosphor layer emits light on irradiation with a vacuum ultraviolet ray generated by AC-glow discharge that takes place between the first and second sustain electrodes in the rare gas.
In the plasma display of the present invention, desirably, the pressure of the rare gas sealed in the discharge space is 1xc3x97102 Pa to 5xc3x97105 Pa, preferably 1xc3x97103 Pa to 4xc3x97105 Pa. When the distance (L0) between the first sustain electrode and the second sustain electrode (to be sometimes referred to as xe2x80x9ca pair of the sustain electrodesxe2x80x9d hereinafter) is less than 5xc3x9710xe2x88x925 m, desirably, the pressure of the rare gas in the discharge space is not less than 1xc3x97102 Pa but not more than 3xc3x97105 Pa, preferably not less than 1xc3x97103 Pa but not more than 2xc3x97105 Pa, and more preferably not less than 1xc3x97104 Pa but not more than 1xc3x97105 Pa. When the pressure of the rate gas is in the above range, the phosphor layer emits light upon irradiation with vacuum ultraviolet ray generated mainly by the cathode glow in the rare gas, and in the above pressure range, the sputtering ratio of each member constituting the plasma display decreases with an increase in the pressure, so that a longer lifetime for the plasma display can be attained.
FIG. 14B schematically shows a light emission state in the plasma display of the present invention when an AC voltage is applied to a pair of the sustain electrodes and when the distance (L0) between a pair of the sustain electrodes is less than 5xc3x9710xe2x88x925 m. The cathode glow B is positioned in the central portion between a pair of the sustain electrodes, and the Aston dark space A appears on each side of the cathode glow B. In some cases, the negative glow can be present partially. When the distance (L0) between a pair of the sustain electrodes is set to be less than 5xc3x9710xe2x88x925 m in the plasma display of the present invention as described above, a discharge mode (cathode glow) entirely different from that in a conventional plasma display can be utilized. Therefore, high AC-glow discharge efficiency can be attained, so that the plasma display can perform with high light-emission efficiency and high brightness. In the plasma display of the present invention, the discharge state shown in FIG. 14A can be also attained by properly setting the distance (L0) between the first sustain electrode and the second sustain electrode (a pair of the sustain electrodes).
The electrically conductive material for constituting the first sustain electrode differs depending upon whether the plasma display is a transmissiton-type or a reflection-type. In the transmission-type plasma display, light emission from the phosphor layer is observed through the second substrate, so that it is not a problem if the electrically conductive material for constituting the first sustain electrode is transparent or non-transparent. However, the address electrode is formed on the second substrate, so that the address electrode is required to be transparent. In the reflection-type plasma display, light emission from the phosphor layer is observed trough the first substrate, so that it is not a problem whether a electrically conductive material for constituting the address electrode is transparent or non-transparent. However, the electrically conductive material for constituting the first sustain electrode is required to be transparent. The term xe2x80x9ctransparentxe2x80x9d or xe2x80x9cnon-transparentxe2x80x9d are based on the transmissivity of the electrically conductive material to light at the wavelength of emitted light (in visible light region) inhererent to the phosphor materials. That is, when an electrically conductive material for constituting the first sustain electrode or for the address electrode is transparent to light emitted from the phosphor layer, such an electrically conductive material can be said to be transparent. Since the second sustain electrode is formed on the upper portion of the side wall on one side of the first separation wall, it is not a problem if the electrically conductive material for constituting the second sustain electrode is transparent or non-transparent. Preferably, the second sustain electrode is made of a material having a low electric resistivity for decreasing the impedance of the second sustain electrode. Non-transparent electrically conductive materials includes Ni, Al, Au, Ag, Pd/Ag, Cr, Ta, Cu, Ba, LaB6, Ca0.2La0.8CrO3, etc., and these materials may be used alone or in combination. Transparent electrically conductive materials includes ITO (indiumtin oxide) and SnO2.
In addition to the first sustain electrode, a bus electrode made of a material having a lower electric resistivity than the first sustain electrode may be formed, on the first substrate, in contact with the first sustain electrode for decreasing the impedance of the first sustain electrode as a whole. The bus electrode can be constituted, typically, of a metal material such as Ag, Al, Ni, Cu, Cr or a Cr/Cu/Cr stacked film. In the reflection-type plasma display, the bus electrode made of the above metal material can be a factor in decreasing the transmission quantity of visible light the is emitted from the phosphor layer and passes through the first substrate, so that the brightness of a display screen is decreased. It is therefore preferred to form the bus electrode to be as narrow as possible as long as the electric resistance value necessary for the first sustain electrode can be obtained.
Preferably, a protective layer is formed on the surface of the first sustain electrode (and also on the surface of the second sustain electrode in some cases). The protective layer can prevent direct contact of ions or electrons with the sustain electrodes, and as a result, the wearing of the sustain electrodes can be prevented. The protective layer works to accumulate a wall charge generated during an address period, works to emit secondary electrons necessary for discharge, works as a resistance to limit an excess discharge current and works as a memory to sustain a discharge state. The material for the protective layer includes magnesium oxide (MgO), magnesium fluoride (MgF2) and aluminum oxide (Al2O3). Of these, magnesium oxide is a suitable material that has chemical stability, shows a low sputtering rate, has high transmissivity in the wavelength of light emitted from the phosphor layer and has a low discharge start voltage. The protective layer may have a stacked structure made of at least two material selected from magnesium oxide, magnesium fluoride and aluminum oxide.
Otherwise, the protective layer may have a two-layered structure. The protective layer having a two-layered structure can be constituted of a dielectric material layer that is in contact with the sustain electrodes, and a covering layer that is formed on the dielectric material layer and has higher secondary electron emission efficiency than the dielectric material layer. Typically, the dielectric material layer is made of a low-melting glass or SiO2. Typically, the covering layer can be made of magnesium oxide (MgO), magnesium fluoride (MgF2) or aluminum oxide (Al2O3). The above two-layered structure can be employed for securing the tranparency of the protective layer as a whole with the dielectric material layer and securing a high secondary electron emission efficiency with the covering layer when the transparency (light transmissivity) of the covering layer in the wavelength region of a vacuum ultraviolet ray is not so high. In the above manner, a stable discharge sustain operation can be attained, and a vacuum ultraviolet ray comes to be absorbed into the protective layer to a less a degree. Further, there can be obtained a structure in which visible light emitted from the phosphor layer is absorbed into the protective layer to a less degree.
Examples of the material for constituting the first substrate and the second substrate include soda glass (Na2O.CaO.SiO2), borosilicate glass (Na2O.B2O3.SiO2), forsterite (2MgO.SiO2) and lead glass (Na2O.PbO.SiO2). The material for the first substrate and the material for the second substrate may be the same as, or different from, each other.
The phosphor layer is made of phosphor materials selected from a red phosphor material, a green phosphor material and a blue phosphor material, and is formed on or above the address electrode. When the plasma display is for a color display, specifically, a phosphor layer made of a red phosphor material (red phosphor layer) is formed on or above an address electrode, a phosphor layer made of a green phosphor material (green phosphor layer) is formed on another address electrode, and a phosphor layer made of a blue phosphor material (blue phosphor layer) is formed on still another address electrode. These phosphor layers that emit three primary colors constitutes one set, and such sets are formed in a predetermined order. A region where a pair of the sustain electrodes and one set of the phosphor layers that emit three primary colors overlap corresponds to one pixel. The red phosphor layer, the green phosphor layer and the blue phosphor layer may be formed in the form of a stripe or a dot.
As a phosphor material for constituting the phosphor layer, a phosphor material which has high quantum efficiency and causes less saturation to a vacuum ultraviolet ray can be selected from known phosphor materials as required. When the plasma display is assumed to be used as a color display, it is preferred to combine those phosphor materials which have color purities close to three the primary colors defined in NTSC, which have good white balance when three primary colors are mixed, which show a small afterglow time period and which can secure that the afterglow time periods of three primary colors are nearly equal. Examples of phosphor material which emits light in red upon irradiation with a vacuum ultraviolet ray include (Y2O3: Eu), (YBO3Eu), (YVO4:Eu), (Y0.96P0.60V0.40O4:Eu0.04) [(Y,Gd)BO3:Eu], (GdBO3:Eu), (ScBO3:Eu) and (3.5MgO 0.5MgF2.GeO2:Mn). Examples of phosphor materials which emits light in green upon irradiation with vacuum ultraviolet light include (ZnSiO2:Mn), (BaAl12O19:Mn), (BaMg2Al16O27:Mn), (MgGa2O4:Mn), (YBO3:Tb), (LuBO3:Tb) and (Sr4Si3O8Cl4:Eu). Examples of phosphor materials which emits light in blue upon irradiation with vacuum ultraviolet ray include (Y2SiO5:Ce), (CaWO4:Pb), CaWO4, YP0.85V0.15O4, (BaMgAl14O23:Eu), (Sr2P2O7:Eu) and (Sr2P2O7:Sn). The method for forming the phosphor layer includes a thick film printing method, a method in which phosphor particles are sprayed, a method in which an adhesive substance is pre-applied to a region where the phosphor layer is to be formed and phosphor particles are allowed to adhere, a method in which a photosensitive phosphor paste is provided and a phosphor layer is patterned by exposure and development, and a method in which a phosphor layer is formed on the entire surface and unnecessary portions are removed by a sand blasting method.
The phosphor layer may be formed directly on the address electrode or may be formed on the address electrode and on the side walls of the second separation wall. Alternatively, the phosphor layer may be formed on the dielectric material film formed on the address electrode or may be formed on the dielectric material film formed on the address electrode and on the side walls of the second separation wall. Further, the phosphor layer may be formed only on the side walls of the second separation wall. The phrase of xe2x80x9cthe phosphor layer is formed on or above the address electrodexe2x80x9d includes all of the above-described embodiments. The material for the dielectric material film includes a low-melting glass and SiO2. When the dielectric material film is formed on the second substrate and the address electrodes, there is a case where the second separation wall is formed on the dielectric material film, and this case is also included in the case where the second separation wall is formed on the second substrate.
The material for the first, second or third separation wall can be selected from known insulating materials. For example, a mixture of a widely used low-melting glass with a metal oxide such as alumina can be used. The separation wall can be formed by a screen-printing method, a sand blasting method, a dry film method or a photosensitive method. The above dry film method refers to a method in which a photosensitive film is laminated on a substrate, the photosensitive film on regions where the separation walls are to be formed is removed by exposure and development and a material for the separation wall is filled in opening portions formed by the removal and is calcined or sintered. The photosensitive film is combusted and removed by the calcining or sintering and the material for the separation wall filled in the opening portions remains to constitute the separation walls. The above photosensitive method refers to a method in which a photosensitive material layer for forming the separation wall is formed on a substrate, the material layer is patterned by exposure and development and then the patterned material layer is calcined or sintered. The separation walls may be formed in black to form a so-called black matrix. In this case, a high contrast of the display screen can be attained. The method of forming the black separation walls includes a method in which the separation walls are formed from a color resist material colored in black.
The rare gas to be sealed in the space is required to satisfy the following requirements.
{circle around (1)} The rare gas is chemically stable and permits setting a high gas pressure from the viewpoint of attaining a longer lifetime for the plasma display.
{circle around (2)} The rare gas has a high radiation intensity of a vacuum ultraviolet ray from the viewpoint of attaining higher brightness for a display screen.
{circle around (3)} The radiated vacuum ultraviolet ray has a long wavelength from the viewpoint of increasing energy conversion efficiency from vacuum ultraviolet ray to visible light.
{circle around (4)} The discharge start voltage is low from the viewpoint of decreasing power consumption.
As a rare gas, He (wavelength of resonance line=58.4 nm), Ne (ditto=74.4 nm), Ar (ditto=107 nm), Kr (ditto=124 nm) and Xe (ditto=147 nm) can be used alone or as a mixed gas. The mixed gas is particularly useful since a decrease in the discharge start voltage based on a Penning effect can be expected. Examples of the above mixed gas include a Nexe2x80x94Ar mixed gas, a Hexe2x80x94Xe mixed gas and a Nexe2x80x94Xe mixed gas. Of these rare gases, Xe having the longest resonance line wavelength is suitable since it also radiates an intense ultraviolet ray having a wavelength of 172 nm.
In the present invention, the glow discharge takes place between the first sustain electrode formed on the first substrate and the second sustain electrode formed on the upper portion of the side wall on one side of the first separation wall, that is, pairs of the sustain electrodes are three-dimensionally arranged unlike a conventional plasma display having pairs of sustain electrodes that are arranged on one plane, so that the discharge cell can be decreased in size.